Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.
A SiConi™ etch is a remote plasma assisted dry etch process which involves the simultaneous exposure of a substrate to H2, NF3 and NH3 plasma by-products. Remote plasma excitation of the hydrogen and fluorine species allows plasma-damage-free substrate processing. The SiConi™ etch is largely conformal and selective towards silicon oxide layers but does not readily etch silicon regardless of whether the silicon is amorphous, crystalline or polycrystalline. The selectivity provides advantages for applications such as shallow trench isolation (STI) and inter-layer dielectric (ILD) recess formation.
The SiConi™ process produces solid by-products which grow on the surface of the substrate as substrate material is removed. The solid by-products are subsequently removed via sublimation when the temperature of the substrate is raised. However, as technology shrinks to 32 nm trench widths and beyond, the dimensions of these solid by-products become non-negligible compared with the smallest dimension of the trench. The appreciable size of the solid by-products may pose challenges relating to ILD recess surface roughness and trench-to-trench variability of the height of the silicon oxide interface.
Methods are needed to reduce surface roughness and height variability in SiConi™ etch processes.